This invention is in the field of propulsive machines cooperating with internal combustion, free piston engines and compressors to produce motive power, lifting, or other uses. This invention also relates to a self-actuated fuel injector that may be utilized in such an engine.
Numerous inventions known in the prior art have been developed, and many proposed which are based on the Newtonian principle of reactive propulsion. Propellers and helicopter rotors, jet engines, and rockets are the principal examples of that genre.
Propellers and rotors, however, require complex internal combustion or gas turbine engines to supply rotating torque to airfoil shaped blades. Large amounts of unconstrained, low pressure air is propelled aftward of the propeller/rotor due to the lift and screw action of the airfoil shaped blades, creating thrust and invoking the concomitant slip, drag, and kinetic energy air stream losses. The total fuel efficiency of these systems is determined primarily by the engine and propeller inefficiencies. In the present invention, there are no propeller losses, and engine losses and engine weight are minimized by the elimination of piston rods, crankshafts, flywheels, transmissions, and, in the case of turbines, high soak temperature turbine blading, adjunct compressors, and internal flow losses.
Chemical thermal-jet engines utilize ram air and axial flow or centrifugal compressors to force air into an engine inlet and raise its pressure in a combustion chamber. In the combustion chamber, fuel is injected and burned creating high temperature, high velocity gases. Part of the gas velocity energy is used up driving turbine blades for the compressor, and the gas then exits a nozzle to produce thrust. Large thermal losses are incurred due to the extreme temperatures at which the jet engine must operate. Rocket engines carry fuel and oxidizer internally and generate their propulsive gasses from within.
Free piston internal combustion engine and compressor combinations are well known, and the prior art contains many examples of various concepts and configurations. None were found which incorporates a power stroke at each end of a single cylinder and uses an unadorned, simple piston whose only functions are to separate the combustion and compression chambers and provide inertial energy storage. Free piston engines and compressors disclosed in the literature are complex and heavy devices which go to great lengths to counteract cylinder reaction to the acceleration of the piston(s) by the use of elaborate spring-counterweight mechanisms or tandem pistons synchronized by rack and pinions, linkages, gears, or other mechanical means.
However, there are no feasible, chambered high pressure propulsion systems that utilize unheated atmospheric air, on a continuous basis, as the main propellant medium. The reason for this is undoubtedly the difficulty of conceiving an engine and compressor combination that is simple and lightweight enough to make it practical.
The present invention involves a major change in the concept of vertical lifting and locomotion in each of the primary modes of land, air, and marine propulsion. As a necessary prerequisite to invention of the atmospheric propulsion engine, the unicycle free piston engine was invented as described herein. The combination of atmospheric air propellant and unicycle free piston engine are part of the unique and defining elements of the present invention.
The single cycle free piston engine disclosed herein uses a simple lightweight piston which minimizes the reactive movement of the cylinder assembly (this movement being a function of the ratio of piston mass-to-cylinder assembly mass).
This present invention is an atmospheric propulsion engine, firing its free piston at each end of the cylinder, scavenging of exhaust products, and natural self cooling due to the large internal ingestion of atmospheric air.
As an indication of the efficacy of the atmospheric propulsion engine, a simple calculation is presented. A cylinder 1.5 inches in diameter, and 18 inches long contains a volume of 31.8 in2 and has a weight of air equal to 0.0014 lbs. at standard atmospheric conditions. When this mass of air is expelled at 70xc2x0 F. (520xc2x0 R), at sonic velocity, in 0.010 seconds through a thrust-producing nozzle, a force of 4.83 lbs. is generated. If this same mass of air is expelled at the temperature and pressure corresponding to a 10 to 1 compression ratio (1300xc2x0 R and 370 psi), the force generated would be 7.71 lbs.
The atmospheric propulsion engine will produce a thrust (force) somewhere between the above numbers, and a computer simulation of the above configuration indicates that an average thrust of 6.4 lbs. can be achieved. Using aircraft type construction, it is estimated that such a device would weigh about 2.1 lbs., yielding an engine thrust-to-weight ratio of 3-to-1. Based on this evaluation, the atmospheric propulsion engine would be suitable for flying and hovering applications, as well as numerous other uses discussed in the following descriptions.
Note: The above performance calculations are based on the following formulas:       Sonic    ⁢          xe2x80x83        ⁢    velocity    =            k      xc3x97      g      xc3x97      R      xc3x97      T      
Where:
k=Ratio of specific heat for air=1.4
g=Gravity constant=386.4 in./sec2 
R=Gas Constant=640 in-lb/lb-xc2x0 F.
T=Temperature xc2x0 R
The specific impulse of the above configuration is calculated to be in the 2000 to 4000 lb-sec/lb range using standard automotive gasoline or diesel fuel.
A comparison of existing art with the present invention of the atmospheric propulsion engine reveals the superior characteristics of the concept and method.
This invention directly converts the fuel""s thermal energy primarily into mechanical Pressure/Volume (PV) forces, compressing atmospheric air and expelling it at sonic velocity to efficiently generate thrust. The only major moving part in the atmospheric propulsion engine system is the internally shared engine/compressor piston which presents another major advantage of this invention, especially in the case of helicopters, by the elimination of noisy and dangerous external rotating propellers and rotor blades.
In the present invention, most of the fuel""s thermal energy is used up in the PV expansion process of the working fluid to drive the piston, thus, after the compressed air propellant is expanded in the thrust nozzles, a relatively cool, benign gas is expelled. No compressor is required as atmospheric pressure is adequate to refill the expulsion gas chamber. However, superchargers, or in applications involving moving vehicles, ram air, can be utilized to raise the compressor inlet pressure, thus enhancing compressor volumetric efficiency and increasing the engine""s thrust-to-weight ratio.
Applications for an independent, free standing thrust engine are manifest.
Given a nominal engine thrust to weight ratio of 3 to 1, coupled with the benignity of the exhaust products, it becomes feasible to design and market a personal passenger vehicle which can fly to its destination without having to concern itself with roads, bridges, or other ground based obstacles. This thrust to weight ratio also may make the engine applicable to xe2x80x9cbackpackxe2x80x9d individual flying machines. Steering, stability and control of such flying machines can be accomplished through thrust vector control mechanisms such as movable nozzles or jet vanes as shown in FIGS. 10 and 11, or may be implemented by other well known aerodynamic means available in the existing art.
Much effort has been expended in the quest for reducing weight and increasing the efficiency of automobiles to combat air pollution. An automobile designed using the lightweight atmospheric propulsion engine disclosed herein would preclude the necessity for flywheels, crankshafts, piston rods, cooling systems, transmissions, driveshafts, differentials, and drive axles. This would eliminate the weight, power losses, and thermal inefficiencies due to these components. Probably, 50% or more of an automobile""s weight could be eliminated and fuel requirements reduced considerably. In addition, the propulsion drive would make vehicle acceleration independent of tire traction. A passenger car could be designed with forward and rearward facing thruster nozzles to control acceleration and braking (thrust reversal, as shown in FIG. 6), and vectored nozzles could control steering to effect a vehicle which is independent of road and tire friction. Or, a hybrid of conventional braking and steering with propulsive drive could be contrived. These same characteristics apply to travel over water, snow, and ice.
Present ground effect machines (GEM) require substantial amounts of air to create sufficient pressure in the vehicle-to-surface interface plenum with which to support the gravity load and provide sufficient surface clearance. This is normally accomplished by the use of large, noisy, inefficient fans. The present invention could be used to provide partial lift from its propulsion engine(s), while using the nozzle exhaust to pressurize the GEM interface plenum. The small plenum back pressure would have little effect on the nozzle""s thrust efficiency.
Aircraft propulsion would benefit from this invention""s enhanced engine specific impulse and from the availability of high speed ram air to increase the propulsion chamber""s volumetric efficiency, thus minimizing the size and weight of the overall propulsion system. The availability of simple, full engine thrust reversal would greatly increase aircraft braking capabilities and reduce runway rollout.
The atmospheric propulsion engine can be slidably mounted to its structure with a simple centering spring mechanism and allowed to traverse a small distance back and forth as shown in FIG. 8. This engine can also be configured in tandem opposed end-to-end combinations to eliminate reactive engine movement, with synchronization being accomplished by a correct starting procedure, metering of fuel, and timing of the ignition process. FIG. 7 shows schematically how two tandem engines could be configured.
In addition to its use in the atmospheric propulsion engine, the simplicity and lightweight of the single cycle free piston engine disclosed herein is desirable for other engine applications such as air compressors and power tools.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.